1. Field of the Invention
The invention relates to a process for applying a spacer of thermoplastic to a glass pane in the course of producing insulated glass panes ii which thermoplastic is applied to a glass pane along its edge.
2. Description of Related Art
In addition to spacers of metal, generally hollow aluminum sections, producing insulating glass with plastic spacers has been known for a long time, there being essentially two embodiments.
One embodiment (xe2x80x9cswiggle stripxe2x80x9d) uses a prefabricated strand of butyl rubber which, withdrawn from a storage reel, is pressed onto one glass pane of an insulating glass pane (DE 37 26 274 C).
Another process (xe2x80x9cBiverxe2x80x9d process) calls for applying a setting plastic to the glass pane from a nozzle which is moved along the edge of the glass pane (EP 0 176 388 A).
Finally, recently it has been repeatedly proposed that thermoplastic spacers be used, generally proceeding such that the thermoplastic is extruded directly onto one glass pane from an application nozzle as a strand with the desired cross sectional shapexe2x80x94generally rectangular (DE 196 32 063 C). In the latter process for producing spacers for insulating glass panes, when the strand which is designed to be used as the spacer is applied, due to the use of thermoplastic, problems arise to the extent that the accurate control of the amount of thermoplastic to be applied is not easily possible. In one known process the attempt is made to use the amount to be applied for accurate proportioning by combination of a plunger pump for delivery of thermoplastic to the nozzle and a gear pump which is provided on the nozzle.
The latter measure (combination plunger pump-gear pump) is not able to ensure under all circumstances that exactly the correct amount of thermoplastic is applied to the glass pane per unit of length of spacer which is to be applied from the nozzle.
The reason for this is that the viscosity, therefore the flow behavior of the thermoplastic, is extremely dependent on temperature. Regardless of the circumstance that insulated lines are used for transport of the thermoplastic heated to a temperature which corresponds to the desired flow behavior to the nozzle, major problems occur when the temperature fluctuates.
Control of the delivery pressure depending on quantity and viscosity in the processing of thermoplastic is known from AT 399 497 B, EP 0 124 188 A and US 4 922 852 A.
The object of the invention is to devise a process of the initially mentioned type with which it is ensured as independently of temperature fluctuations as possible that the correct amount of thermoplastic is applied at the time to form a spacer for insulating glass panes.